1. Field of the Invention
The present invention relates to a battery control device, and more particularly, to a battery control device that includes a self-diagnostic function of a battery system.
2. Description of the Related Art
Electric vehicles and plug-in hybrid vehicles (PHV) have become commercially practical and various types of vehicles are introduced on the market. Such vehicles use electric power as a power source. Those vehicles are equipped with an idle stop function so as to improve the rate of fuel consumption. In such vehicles, it is highly important to ensure reliability of a system, that is, reliability of a battery unit including a battery control device. In the battery control device, a self-diagnostic function is performed to keep track of occurrences of abnormalities.
FIG. 1 is a block diagram illustrating a controller (central processing unit (CPU) 110) of a battery system that includes a known self-diagnostic function. FIG. 2 is a flowchart illustrating processing of the self-diagnostic function performed by the CPU 110, and illustrates the processing mainly focusing on processing for detecting abnormalities in a current measuring system.
After a current variation is predetermined with respect to an obtained variation in voltage of a battery V, the CPU 110 detects an abnormality in accordance with the predetermined current variation. Specifically, the CPU 110 starts self-diagnosis of a measuring system (S110). When an ignition 130 is OFF (N at S112), the CPU 110 performs processing for detecting a prescribed variation in voltage (S114). When the CPU 110 detects the prescribed variation in voltage (Y at S114), the CPU 110 performs processing for detecting whether a discharge current is below a prescribed value (S116). When the discharge current is below the prescribed value (Y at S116), the CPU 110 determines that an abnormality has occurred in a current measuring system 120 (S118).
Self-diagnostic techniques have been known that can detect degradation in a secondary battery or abnormalities in a measuring system in such a battery system (refer to Japanese Patent Application Laid-open No. 2010-200574, for example). Specifically, in the technique disclosed in Japanese Patent Application Laid-open No. 2010-200574, the state of charge (SOC) of a secondary battery is calculated by integrating currents detected by a current measuring unit, and open-circuit voltages of the secondary battery at predetermined first and second timings are estimated as first and second open-circuit voltage values on the basis of measured values from a voltage measuring unit and the current measuring unit. Subsequently, first information about the amount of charge/discharge of the secondary battery is obtained on the basis of first and second SOCs at the first and the second timings, second information about the amount of charge/discharge of the secondary battery is obtained on the basis of first and second open-circuit voltage values at the first and the second timings, and whether abnormalities are present in the secondary battery, a voltage detecting unit, and a current detecting unit is determined on the basis of the first and the second information.
The conventional technique illustrated in FIG. 1 and FIG. 2 is based on the premise that a voltage measuring system is normal. As a result, there has been a problem in that, even when it is determined that an abnormality has occurred, the abnormality cannot be distinguished whether it relates to the voltage measuring system or the current measuring system. The same holds true for the technique disclosed in Japanese Patent Application Laid-open No. 2010-200574. Consequently, self-diagnostic processing for detecting abnormalities has been increased, which complicates the processing and also limits the number of timings of the self-diagnostic processing. Thus, an alternative technique has been needed.